The present invention relates to stabilization of halogen containing polymers containing more than 5 weight percent halogen so as to provide improved heat and light stability therefor. Although not limited thereto, the present invention will be particularly described with respect to the stabilization of vinyl or similar polymers derived from vinyl chloride, vinyl chloride acetate, vinylidene chloride, chlorostyrene or chlorobutadiene. The present invention is also applicable to resins which are post-halogenated or which are copolymerized with chlorinated or halogenated unsaturated hydrocarbons or their compounds, such as chlorinated polyethylene or its homologs and polymers, or chlorinated butadiene or styrene and their homologs and polymers.
It is known that chlorine containing resins such as polyvinyl chloride in which more than 5 weight percent chlorine is contained in the resin tend to be unstable toward the action of heat and light. Decomposition of the resin takes place unless temperatures used during formation and fabrication are kept below the temperature at which color formation begins. Currently available metallic stabilizer systems generally suffer from one or more of the following disadvantages: They are toxic (tin, barium and cadmium containing compositions). Upon utilization of certain stabilizers poor clarity of the polyvinyl chloride results (calcium and zinc containing salts). Some stabilizers are characterized by high cost (tin, barium, cadmium and calcium containing compositions). With many stabilizers currently commercially available, relatively low levels of stability are obtained by their use and even where large amounts are incorporated into the polyvinyl chloride, the efficiency of such stabilizers leaves much to be desired.
It is well known that calcium and zinc carboxylic acid salts function as stabilizers for polyvinyl chloride. Dihydrocarbyltin aliphatic-substituted succinates are discloses in U.S. Pat. No. 3,068,195 as useful to provide vinyl halide compositions which show improved resistance to light and heat.
The discoloration of polyvinyl chloride is thought to be due to liberation of hydrogen chloride which catalyzes further decomposition of the resin. The addition of basic compounds to neutralize the hydrogen chloride to form inert compounds should theoretically retard such discoloration and darkening. It has been found that many basic compounds are unsatisfactory and other similar compounds do not give the desired results as indicated by substantial darkening of the resin upon exposure to heat.
For example, lead, cadmium, manganese and calcium salts of high molecular weight, fatty acids, such as oleic, lauric, and palmitic; lead and cadmium salts of lower molecular weight fatty acids, such as the acetates; organic and inorganic bases, such as hydroxyl-amine and hexamethylene tetramine; alcoholates of alkali earth metals, such as calcium 2-ethyl hexylate; and calcium and cadmium salts of hexoic acids, when both an alkyl group or an ethyl group and a phenyl group are directly attached to the alpha carbon atom, such as calcium phenylethylhexoate, cadmium pehnylethylhexoate and lead phenylethylhexoate, will permit substantial yellowing or darkening. The same is also true of cadmium salts of hexoic acid where an ethyl group only is attached to the alpha carbon atom. In general lead and cadmium salts are unsatisfactory and the same is true of alkali metal salts. Calcium, strontium and barium salts of straight chain unbranched acids or where the branched acid has a phenyl or aryl group attached directly to the alpha carbon atoms are also not entirely satisfactory.
The same difficulty has also been experienced with organo tin oxides or hydroxides; tetra-ethyl or tetra-butyl tin compounds; tetra-phenyl or propyl tri-phenyl lead and tin compounds; and dibutyl, tributyl and diphenyl tin acetates; oleates, laurates or stearates. Although these materials are useful in stabilizing halogen-containing vinyl resins, nevertheless incorporation of these materials does not prevent development of yellow color and eventual darkening or blackening of the resins, and furthermore use of these materials frequently results in development of a haze in heat pressed sheets.
With an adequate stabilizer incorporated into the polyvinyl chloride, an increased processing temperature can be utilized making possible high speed fabrication, including injection molding, extrusion, and blow molding of rigid polyvinyl chloride. The degradation noted upon exposure of polyvinyl chloride to elevated processing temperatures appears to result from a thermaloxidative dechydochlorination. Stabilizers have been incorporated into the polymer in order to retard or delay the initiation of propagation of the dehydrochlorination as well as to scavenge or react with the evolved hydrogen chloride. As indicated above, the stabilizers commonly used in the past have not been entirely satisfactory, and therefore it is the objective of the present invention to provide a process for the stabilization of compositions of polyvinyl halide having improved heat and light stability.
It is known to react an alpha-olefin with maleic anhydride to obtain an alkyl succinic anhydride. Such compounds, while having such varying uses as curing agents for epoxy resins, rust inhibitors, de-emulsifying agents, fungicides, plasticizers and surfactants, etc., have not been suggested for use either alone or further reacted as described herein as stabilizers for halogen containing resinous materials to reduce the tendency of these resins to discolor upon exposure to heat and light.